3-item Likert-scale: "How do you rate overall pain relief with the drug?" with 3 possible answers: "very effective", "effective", or "ineffective". The average of ratings at visits 2-5 was calculated as median, rounded up to the closest integer.

Percentage Difference Between WOMAC Pain Subscale Score From Baseline to the End of the Study (Week 12) [ Time Frame: Baseline to week 12 ] [ Designated as safety issue: No ]

Percentage of difference in WOMAC Pain Subscale score between baseline and week 12. The WOMAC scale is a 24-item questionnaire divided in 3 subscales, using a 100mm visual analog scale ranging from no pain (0mm) to extreme pain (100mm). The WOMAC Pain Subscale results from the sum of 5 questions.

Percentage Difference Between WOMAC Physical Function Subscale Score From Baseline to the End of the Study (Week 12) [ Time Frame: Baseline to week 12 ] [ Designated as safety issue: No ]

Percentage of difference in WOMAC Physical Function Subscale score between baseline and week 12. The WOMAC scale is a 24-item questionnaire divided in 3 subscales, using a 100mm visual analog scale ranging from no pain (0mm) to extreme pain (100mm). The WOMAC Physical Function subscale results from the sum of 17 questions.

Percentage of difference in WOMAC Pain Subscale score between baseline and intervening visits 2-4. The WOMAC scale is a 24-item questionnaire divided in 3 subscales, using a 100mm visual analog scale ranging from no pain (0mm) to extreme pain (100mm). The WOMAC Pain Subscale results from the sum of 5 questions.

The Investigator Global Rating of Pain is a 3-item Likert-scale to answer the following question: "How do you rate this patient's overall pain relief with the drug?" with 3 possible answers: "very effective", "effective", or "ineffective".

Percentage of Participants Who Dropped Out From Trial by Dropout Reason [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]

Reasons for withdrawal from the trial were collected and the percentage of participants who dropped out from trial were calculated by dropout reason

Males or Females between the ages of 40-75 with a diagnosis of moderate to severe osteoarthritis of the knee, consistent with the American College of Rheumatology (ACR) Clinical Classification Criteria for Arthritis of the Knee:

Current knee pain

Less than 30 minutes of morning stiffness with or without crepitus on active motion.

Confirmation either by arthroscopy or radiologist's report (X-rays showing osteophytes, joint space narrowing or subchondral bone sclerosis {eburnation}) within five years prior to entry into the study.

Treatment within the last 3 weeks with any of the following medications: monoamine oxidase inhibitors; tricyclic antidepressants and other tricyclic compounds (e.g. cyclobenzaprine, promethazine); neuroleptics; selective serotonin reuptake inhibitors; or any other drug that reduces seizure threshold.

Treatment with another investigational agent within the last 30 days.

A history of seizure disorder other than Infantile Febrile Seizures.

Previous or current opioid dependency.

Bowel disease causing malabsorption.

Pregnancy or lactating or childbearing potential and unwilling to utilize a medically approved method of contraception during participation in this clinical trial.

Significant liver disease, defined as active hepatitis or elevated liver enzymes >3 times the upper boundary of the normal range.

Allergy or adverse reaction to tramadol or any structurally similar drugs e.g. opiates.

Any other condition, that, in the opinion of the Investigators, would have adversely affected the patient's ability to complete the study or its measures.

Contacts and Locations

Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study.
To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below.
For general information, see Learn About Clinical Studies.